This proposal is composed of three separate projects. They represent three approaches to a better understanding of human immune responses in general, and cellular immunity in particular. The work is concerned with the developmental regulatory and pathological aspects of animal and cellular immune responses. The first project consists of an analysis of the cellular mechanisms involved in the control of delayed hypersensitivity using desensitized quinea pigs as a model. When quinea pigs are given a large dose of immunogen shortly after immunization, cell mediated immune responses to all antigens are temporarily reduced. An attempt to understand this mechanism we hope will lead to information concerning the mechanisms of anergy in some human diseases. The second project concerns an analysis of the distribution and function of thymus derived and bone marrow derived lymphocytes in human diseases associated with energy caused by either disease process or drugs. In this project, we have studied lymphocytes in diseases such as leprosy and sarcoidosis and in patients receiving immunosuppressive agents following transplantation. The third study consists of an analysis of the dose dependent effects of immunosuppressive agents on immune capacity in an attempt to establish guidelines in man for therapeutically selective suppression of a particular facet of immune response.